the systematic description of landforms

The Systematic Description of Land FormsAuthor(s): W. M. DavisSource: The Geographical Journal, Vol. 34, No. 3 (Sep., 1909), pp. 300-318Published by: The Royal Geographical Society (with the Institute of British Geographers)Stable URL: http://www.jstor.org/stable/1777147 .Accessed: 24/03/2014 04:32

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

The Royal Geographical Society (with the Institute of British Geographers) is collaborating with JSTOR todigitize, preserve and extend access to The Geographical Journal.

http://www.jstor.org

This content downloaded from 128.103.149.52 on Mon, 24 Mar 2014 04:32:29 AMAll use subject to JSTOR Terms and Conditions

300 THE SYSTEMATIC DESCRIPTION OF LAND FORMS. 300 THE SYSTEMATIC DESCRIPTION OF LAND FORMS.

the case. It should be swung in a horizontal plane as high above the ground as practicable, without climbing eminences higher than ant-heaps. Naturally, the reading will be made immediately on the instrument being brought to rest. Some care must be exercised in doing this, as a chuck upwards will cause the mercury to rise in the tube.

In hot countries like the Sahara, where the radiation from the soil is very great, the air may be superheated by the radiation to relatively considerable heights. Accord- ing to Prof. W. E. Thrift, in such regions the variation of temperature'with height would perhaps be considerable, particularly so near the ground. The main effect would probably arise from convection currents, though these might tend towards equalization, but it is not quite obvious whether their effect would be relativrely greater in hot than in cold countries.

Experiments are wanting to show the results of variation of height. It is advis- able, then, that a certain height above the soil, say 6 feet, should be adopted by all observers with a view to uniformity.

A recent experiment * by Prof. R. W. Wood has a very direct bearing on the subject here considered. He finds that the heat in greenhouses is not, as commonly supposed, caused by a lengthening of the heat-waves which impedes their return passage through the glass, but is essentially due to the imprisonment of the mass of heated air. It will thus be seen how important it becomes to construct a chamber which will not in the least interfere with free circulation, for in the normal state in the open the air is in constant motion, and that motion is nowhere greater than in the tropics.

It is hoped that the considerations above advanced may lead to unification of method with a concomitant increase of accuracy, and that these notes may be especially of assistance to those observers who have little leisure for study in the press of administrative duty.

THE SYSTEMATIC DESCRIPTION OF LAND FORMS. t By Prof. W. M. DAVIS, Harvard University.

ONE of the most serious tasks of the geographer is the preparation of accurate and intelligible descriptions of the forms of the lands. The earlier method employed in such descriptions was essentially empirical, in that it made no attempt at explanation; its terms, including such words as hill, valley, mountain, plain, river, lake, gave no indication of origin for the features that they named. But in association with these terms were certain others, such as delta, dune, volcano, lava-flow, sea-cliff, which always gave a suggestion of origin. The introduction of terms of the second class was a natural result of the increase of geological knowledge, whereby the existing features of the Earth's surface are more and more clearly seen to result from the action of ordinary processes through long periods of time.

To-day a belief in the reasonable production of land-forms has become so general, that the question may fairly be asked, whether it is not now possible to develop a method of thorough-going- explanatory description, which shall treat all land-forms in view of their origin. I have been experimenting on the development

the case. It should be swung in a horizontal plane as high above the ground as practicable, without climbing eminences higher than ant-heaps. Naturally, the reading will be made immediately on the instrument being brought to rest. Some care must be exercised in doing this, as a chuck upwards will cause the mercury to rise in the tube.

In hot countries like the Sahara, where the radiation from the soil is very great, the air may be superheated by the radiation to relatively considerable heights. Accord- ing to Prof. W. E. Thrift, in such regions the variation of temperature'with height would perhaps be considerable, particularly so near the ground. The main effect would probably arise from convection currents, though these might tend towards equalization, but it is not quite obvious whether their effect would be relativrely greater in hot than in cold countries.

Experiments are wanting to show the results of variation of height. It is advis- able, then, that a certain height above the soil, say 6 feet, should be adopted by all observers with a view to uniformity.

A recent experiment * by Prof. R. W. Wood has a very direct bearing on the subject here considered. He finds that the heat in greenhouses is not, as commonly supposed, caused by a lengthening of the heat-waves which impedes their return passage through the glass, but is essentially due to the imprisonment of the mass of heated air. It will thus be seen how important it becomes to construct a chamber which will not in the least interfere with free circulation, for in the normal state in the open the air is in constant motion, and that motion is nowhere greater than in the tropics.

It is hoped that the considerations above advanced may lead to unification of method with a concomitant increase of accuracy, and that these notes may be especially of assistance to those observers who have little leisure for study in the press of administrative duty.

THE SYSTEMATIC DESCRIPTION OF LAND FORMS. t By Prof. W. M. DAVIS, Harvard University.

ONE of the most serious tasks of the geographer is the preparation of accurate and intelligible descriptions of the forms of the lands. The earlier method employed in such descriptions was essentially empirical, in that it made no attempt at explanation; its terms, including such words as hill, valley, mountain, plain, river, lake, gave no indication of origin for the features that they named. But in association with these terms were certain others, such as delta, dune, volcano, lava-flow, sea-cliff, which always gave a suggestion of origin. The introduction of terms of the second class was a natural result of the increase of geological knowledge, whereby the existing features of the Earth's surface are more and more clearly seen to result from the action of ordinary processes through long periods of time.

To-day a belief in the reasonable production of land-forms has become so general, that the question may fairly be asked, whether it is not now possible to develop a method of thorough-going- explanatory description, which shall treat all land-forms in view of their origin. I have been experimenting on the development

* Phil. Mag., February, 1909. t Research Department, March 18, 1909. * Phil. Mag., February, 1909. t Research Department, March 18, 1909.


THE SYSTEMATIC DESCRIPTION OF LAND FORMS. 301

of such a method for some time,* and believe that it is, in various ways, more useful and more effective than the older-fashioned empirical method, or than the half-hearted, accidentally explanatory method. As at present developed, it may be called the method of structure, process, and stage.

Every feature of the land may be treated as the surface form of a certain structural mass, accumulated under certain past geological conditions, and placed by crustal movements, with more or less deformation, in a certain attitude with respect to baselevel, so that it comes to Ie acted upon by various external destructive processes, which have now carried forward their changes to a certain stage of development. This is only the simplest outline of the method, which may now be illustrated by certain actual examples before proceeding to its complications.

Along the Adriatic coast of Italy, near Ancona (but not including the rocky hills immediately south of this city), the marginal ridges of the Apennines are bordered by a series of imperfectly consolidated sandy and clayey marine strata dipping gently seaward, and originally possessing a smoothly sloping surface, as shown in the background of Fig. 1, which would have deserved the name of

?~~~~~~~~~~~~?

302 THE SYSTEMATIC DESCRIPTION OF LAND FORMS.

stand in a nearly straight line for many miles, although interrupted by numerous valleys. No deltas are to be expected at the mouths of such valleys, because the whole shore-line must be regarded as having retreated.

All of these features alre concisely expressed by saying that the Adriatic border of Italy, near Ancona, consists of a coastal plain of imperfectly consolidated sands and clays, which has reached a stage of late mInature dissection under the action of normal and marine erosional processes. The term " coastal plain " implies that the strata of which the district consists were laid down as marine deposits, sloping gently away from the land mass from which they were derived; also that they were revealed by a broad uplift which did not significantly disturb their simple structure. The phrase, "imperfectly consolidated sands and clays," gives us to understand that no resistant layers are present which might outcrop in ledges, and thus form falls in the streams or break the even slope of the valley-sides. The brief mention of " normal and marine processes" informs us sufficiently as to the destructive agencies that have been at work on the plain since its uplift. Under "( normal processes" we understand the ordinary action of weathering and washing; the streams erode their valleys, and the valley-sides waste under the attack of the weather; the main streams must necessarily be extended forward from their former mouths, and take courses consequent on the slope of the plain to the new shore-line; minor streams must rise on the plain itself, and run down the slope of the plain to the sea; on the sides of the valleys eroded by these consequent members of the drainage system, small branch streams must be established in irregular courses, and these may therefore be called insequent. Under "marine processes," we understand the action of sea-waves and currents, which actively attack the shore, cutting it back in a cliff; at the same time they slowly wear the bottom, gradually giving it an increasing depth. The significant words, " late mature dissection," indicate at once that both of the erosional processes, normal and marine, are well advanced in the series of changes which have, as a goal, the complete destruction of the coastal plain. The main streams must in late maturity have opened wide-floored valleys; the side streams must branch elaborately, thus dissecting the original plain into a multitude of hills and spurs; the axes of the hills and spurs must trend in a general way toward the coast, because the streams which have carved the valleys between the hills must for the most part have had their courses determined, directly or indirectly, by the initial slope of the plain; the hills must have been weathered into smoothly arching crests and smoothly sloping sides; the shore-line must havc been cut back so as to truncate the hills in cliffs, all standing in line. T'hus a general mental image of the district may be formed, in which all the features are systematically correlated, because they are all described as having originated by the action of definite processes on a comprehensible initial form, and because the action of the processes has gone on to an assigned stage of development.

'l'wo features, shown on a larger scale in Fig. 2, remain to be described. The broad, late mnature, main valley-floors are not flat, but are found to be moderately terraced as one advances inland; and the shore-line does not now lie along the base of the mature cliffs, but along the outer side of a sandy strand-plain, 100 or 200 metres wide. T'he terraces are evidently the result of a recent and gentle slanllting uplift, after the valleys had been maturely widened; and judging by the height of the terraces, the uplift seems to have increased from zero near the coast-line to 10 or 15 metres at the inner border of the plain. Perhaps half or mlore of the former valley- floors has been consumed in the excavation of the newer and lower valley-floors, so that the present flood-plains in the main valleys are of somewhat greater area than the terrace remnants of the former flood-plain. The strand-plain is evidently the result of a recent change in the action of the shore-waves. From having acted



as erosive agents for a time long enough to cut the mature cliffs, they have for a briefer time acted as constructive agents, and have built forward a low and narrow belt of sand; in other words, after having maturely retrograded the cliffs, the waves have prograded the strand-plain. The strand-plain broadens a little opposite each valley, for now that the shore-line is prograding, the rivers have opportunity of building their deposits forward; but no sharp deltas are seen, because the 'long- shore action of the waves and currents distributes the river-brought waste all along thle front of the strand-plain.

There is good reason for regarding the action of the streams in terracing or degrading the former valley-floorls as the cause of the progradation of the strand- plain. The slanting uplift revived the mature streams, and caused them to degrade the valleys through which they were previously flowing contentedly; the degrada- tion of the valley-floors increased the quantity of waste washed out from the river- mouths, and thus compelled the waves to abandon their former task of cliff cutting

FIG. 2.-BLOCK DIAGRAM OF A COASTAL PLAIN WITH A TERRACED VALLEY AND A STRAND PLAIN.

or retrograding, and for a time at least to take up the contrary task of distributing the river-waste along the shore, thereby building forward or prograding the strand- plain. The previous description may therefore now be expanded and supplemented as follows :-the coastal plain of imperfectly consolidated sand and clay strata had reached a stage of late maturity by normal and marine erosion, when a gentle slanting uplift occurred, which caused the extended consequent streams to terrace the main valley-floors, and the waves and currents to prograde the shore-line. If any doubt is felt on the correlation of these features, it may be indicated by the cautious words, as if. After the coastal plain had been dissected to a stage of. late maturity, its broad valley-floors were gently terraced, and its shore-line was prograded, as if a gentle tilting uplift and revival of stream erosion had taken place. When this stage of general description is reached, individual elements, such as length, breadth, and height, may be added, and villages and lines of travel may be appropriately located. If such details are introduced before the general features are sufficiently presented, they are lost in a confusion of half-understood forms.



Certain general considerations may now be mentioned. First, it may be pointed out that only so much of past history, or what may be properly called geology, is introduced as will be of direct service in reaching an understanding of present form. Other geological information, however important and interesting in itself, is irrelevant, and shouldl be omitted. Second, the slight complication caused by uplift, after late maturity of dissection had been reached, is significant, for it illustrates what often happens, namely, the occurrence of a movement of the land-mass during the progress of its sculpture, whereby the cycle of erosion, until then current, is interrupted and a new cycle is introduced. " Interruption" of a cycle may therefore always be used in a somewhat technical sense to indicate a crustal movement whereby the land- mass has been placed in a new attitude with respect to baselevel. In the case of the Italian coastal plain, the itlJterruption was a slight one, causing hardly more than an episode in the former cycle instead of introducing a new one. In the following case a more se!ious interruption is considered.

Eastern Virginia and Maryland, typified in Fig. 3, contain a maturely dissected coastal plain, recently somewhat depressed. The new cycle thus introduced has not passed beyond early youth. A useful picture of the essential featulres of the

-~~~

- "B

FIG. 3.-BLOCK DIAGRAM OF A MATURELY DISSECTED COASTAL PLAIN, RECENTLY HALF SUBMERGED.

district concerned may be constructed from this brief explanatory description. The structure of the district will be understood from the term coastal plain, which means, as already stated, that the area is made up of stratified deposits sloping very gently toward the ocean from an older land of other structure in the background. The chief features of surface form may be inferred from the phrase, maturely dissected; for this implies, as before, the presence of main and subordinate consequent streams, with many insequent branches, and of well-opened valleys, with sides that slope gently down from rounde: hill-tops. When this stage in the cycle was reached, its further normal progress was interrupted by a movement of depression, thus placing the mass in a new attitude with respect to baselevel, and introducing a new cycle of erosion. The maturely dissected coastal plain having been somewhat lowered, its main valleys and many branch valleys are necessarily partly submerged, and converted into long irregular branching bays of very sinuous shore-line; and the new shore-line thus produced is as yet but little modified by wave cutting and delta filling, the modification being more along the outer coast and at the chief bay-heads, where the ocean waves and the larger rivers are at work, and less in the bays where only the weaker waves and the



smaller streams are in action. The effective picture thus sketched may now receive as many additional touches as are desired in the way of length, breadth, height, and individual features. Various complications in the history of the district, con- cerning which discussion is still going on, are not here referred to.

It must be manifest from the two foregoing examples that the method under consideration involves a scheme of description and not a plan of investigation. The chief events in the geological history of a district, in so far as theybear on its form, must be found out before the method of explanatory description can be applied. Nevertheless, the method is helpful in investigation, first by indicating the kind of results that must be searched for, and second by indicating the k ind of results that are irrelevant in the geographical sense, and therefore better omitted than included in a geographical description. One who is familiar with recent articles on the geomorpho- logical aspects of physical geography must have noticed that the attention of the reader is often distracted from features of present form by the introduction of unessential matters of past history, with the result of making the description geological rather than geographical. If the intention of the writer is to give an account of past changes in their chronological sequence, it is proper enough to focus the attention on the passage of past time; but if the intention is to give an explanatory description of existing forms, it is important not only to

exclude all matter that

has not a helpful relation to existing forms, but to present the explanation of exist-

ing forms in such a way as to direct attention to them as the present product of

past processes, not to the processes themselves; and in this respect the systematic

method here presented may be of much practical assistance. It is also clear that the systematic method is not completely self explanatory;

it

involves a special terminology of which an understanding must be gained before the

method can be serviceable. For example, the phrase, " maturely dissected," can be

properly appreciated only after the general scheme of the cycle of erosion has become

familiar; but as the scheme of the cycle of erosion has now been before the geo-

graphical public for at least ten years, it is not necessary to regard it as a novelty

any longer. Again, the effect of submergence in transforming valleys into bays

must be recognized before the phrase, "recently somewhat depressed," can gain its

full value; but the idea here involved is so simple that the wonder is that geography

had to wait until the latter half of the nineteenth century for its introduction. A third example may be taken from the western slope of the central

massif

of France, in the neighbourhood of the valley of the Lot. This district, of which a

diagram is given in Fig. 4, may be described as a maturely dissected plateau of

indurated horizontal strata, in which the valleys of the smaller consequent and

insequent streams show the work of only one cycle, while the main valley of the Lot

shows the work of two, in the first of which the late-mature meandering river had

nearly consumed its valley-side spurs; and in the second, introduced by a moderate

uplift, the river has now consumed about half of the previous flood-plain in reaching

maturity again. The mental picture of the district, constructed from this descrip-

tion, must embody a great number of rounded hills of equable height, divided

by many irregularly branching valleys; for in a plateau of horizontal strata, most

of the drainage must be insequent, without systematic control, and hence following

no definite direction. The hillside slopes, smoothly covered with creeping waste,

must descend with gracefully curved profiles to the narrow valley-floors of the well-

graded smaller streams. But the main valley of the Lot must be conceived as

broadly oper.ed and as showing a well-defined, gravel-covered terrace (horizontal

lines, Fig. 4), below which the curving river has eroded a narrower valley, with well- developed and systematically placed flood-plain scrolls (dotted, Fig. 4). Rock out- crops are to be expected only along the outer side of the river

curves, where the

No. III -SEPTEMBER, 1909.] y


306 THE SYSTEMATIC DESCRIPTION OF LTAND FORMIS.

valley-side amphitheaters are being enlarged, and along the down-valley side of the curves, where the up-valley side of the terrace-spurs (not seen in Fig. 4) is being worn away. The reason for the visibility of the work of two cycles in the main valley is evidently that the main river works rapidly; it had developed a late- mature or broad-floored valley in the first cycle, when the branch streams had

FIG. 4.-BLOCK DIAGRAM OF THE TERRACED VALLEY OF THE LOT IN WEST- CENTRAL FRANCE.

eroded only early mature or narrow-floored valleys; now in the second cycle, the branch streams have deepened their valleys and have become mature enough to destroy practically all traces of the former floors; while the main stream, although already more mature than the side streams, has not yet widened its new valley- floor sufficiently to consume all of its still broader, earlier valley-floor.

FIG. 5.-BLOCK DIAGRAM OF A MEANDERING VALLEY WITH SHARPENED SPURS, OCCUPIED BY AN UNDERFIT STREAM.

An interesting variant on Fig. 4 is given in Fig. 5, in which the curves of the valley-sides between the sharpened spurs indicate that the valley was given essentially its present form by a river of good size, whose curves were of the same dimensions as those of the valley-sides, as is the case in Fig. 4; yet at present the slender stream by which the valley is drained wanders about most irregularly on the valley



floor in curves of much smaller pattern. Such an abnormal relation between valley and stream often occurs; it may be concisely presented by first describing, inl terms of flood-plain breadth, curve radius, and spur-trimming, the stage of development reached by the valley, and then describing the stream that drains it, in terms of breadth and curve radius. It seems clear in such a case that the original valley- cutting stream must have been much reduced in volume. In its present reduced volume it may be described as a misfit or an underfit stream.

It is manifest that the features summarized in Figs. 4 and 5 can be, as before, best appreciated if the observer or the reader has already made a systematic study of an entire series of appropriate ideal forms, developed in regular order. In the case of a plateau, for example, certain naturally associated forms characterize the youthful stages of its dissection; other forms, the mature stages; still other forms, the old stages. It will evidently be of much practical benefit to an observer who has to describe plateau forms, if he has previously gained familiarity with the whole series of changes through'which a plateau passes in the course of a normal cycle of erosion; he may then most concisely describe an actual case as corresponding to a particular member of the series of ideal cases; and all his readers, who are familiar with the same scheme, will immediately apprehend his meaning. In this respect, the scheme of description here recommended is practically serviceable because it greatly increases the number of ideal forms with which the observer is equipped, and in terms of which the actual forms that he finds may be described. The ideal forms are, moreover, easily apprehended and remembered, because all their parts are reasonably developed and associated. In the same way, the beautiful series of ideal forms developed during the erosion of a valley by a meandering river must be studied out, and the terms used in their description must be known, before the use of the terms in a description can summon up the desired forms. Actual forms of this kind frequently occur; it is therefore fitting that an effective terminology for their description should be introduced; and the most effective terminology yet suggested is based on the sequence of valley forms that is systematically developed during the progress of an undisturbed cycle of erosion.

Another advantage of the explanatory method is the ease with which a simple series of ideal forms, such as those of the plateau series above mentioned, may be expanded into a more elaborate series, so as to fit a much larger variety of natural cases. In the first place, a plateau mass of horizontal structure may be conceived as consisting of resistant and weak strata in any order; a group of resistant strata between two groups of weak strata, as in Fig. 6; or a group of weak strata between two groups of resistant strata, as in Fig. 7; or many alternations of resistant and weak strata, as in Fig. 8; and so on. The general plan of development being, once understood, all the particular features that will be associated with each particular structure may be easily deduced. In the second place, a plateau of any special structure may, at the beginning of its cycle of erosion, stand high or low; the relief developed by its dissection will evidently be strong during the youth arnd maturity of the first case, as in Fig. 8, but can never be strong in the second case, as in Fig. 9. Finally, the texture of dissection-that is, the spacing o' the streams and their valleys and the resultant breadth of the hills and spurs-may vary according to certain conditions, the chief of which are the perviousness of the plateau mass, or at least of its soil cover, and the climate under which its dissection takes place. Pervious strata allow much of the rainfall to enter the ground and thus diminish the number of small branch streams; as a result, the texture of dissection is coarse, and the hills are broad and full bodied, as in Fig. 11. If the strata are impervious and of fine- grained materials, and if the climate is so dry as to make vegetation scanty, then the texture of dissection during youth and early maturity will be very fine, and the

Y2



surface will assume a " bad-land " quality, with innumerable little hills and spurs between innumerable little valleys, as ill Fig. 10. Thus the scheme of description

really contains five elements: struc- _-?^]3__- iture, process, stage, relief, and

_^^P^^^ , /1^^^^^Lj^~ ~texture; all require consideration, ^^^^-^^^n~~ - but the first three suffice when

\ \\'S'^ ---~~/6 giving the scheme a name.

^\ . = L = %


of normal erosion, and as having been reduced to dome-like masses, with rounded ridges and spurs sprawling irregularly between well-opened valleys; outcropping ledges must hlave been rare or wanting, because subdued mountains must always be pictured as very generally covered with a creeping sheet of rock-waste; lakes and waterfalls must have been absent, because such features are destroyed by the late mature development of the streams and valleys; and all the side valleys must be thought of as joining the main valleys at accordant grade, because even if dis- cordant or hanging valley junctions had occurred in an early stage of the normal cycle, accordant valley junctions must necessarily have been developed by the time the mountains between the valleys had been subdued.

i" tlll i \i a \ 11t 1tl ilIl

FIG. 12.-DIAGRAM OF SNOWDON, NORTH WALES.

The mountain group thus fashioned then suffered submature glaciation, and this necessarily introduces many changes. All the normal valley heads will be enlarged and converted into cwms; the cwm-head cliffs will, in a submature stage of glaciation, be retrogressively eroded so far into opposite sides of the subdued mountain domes as to consume parts of the intervening rounded mass, and to convert them into sharply serrated ar8tes; the cwm-floors may be so well deepened as to hold small rock-basin lakes; the broadened floor of the cwms, as well as of the smaller lateral valleys, will descend by a strong slope into the larger valleys, which have been de epened and broadened as glacier troughs; thus the cwms as well as the side valleys will come to stand over, or to " hang," with respect to the deepened main valleys (or glacial troughs); and the deepened main valley-floors, being only in a submature stage, may exhibit various inequalities, here scoured out a little deeper so as to'hold a lake; there unevenly worn down so that a rock-step interrupts the valley slope; and again showing immature lateral scouring, so that knot s, ledges, and cliffs are locally abundant along the valley-sides. Finally, as the submature glaciation is described as recent, the changes since a normal climate has been re- established must be small; the cwm-head cliffs will have weathered somewhat, so that slopes of waste (screes) accumulate at their base; the cwm-floor basins may be partly converted into bogs; the front steps of the cwms and of the hanging lateral valleys may be somewhat cleft by normal stream action; deltas will be growing in the valley-floor lakes, gorges will be partly eroded in the rock-steps, and slopes of waste will be forming under the valley-side cliffs. But as the glaciation



is explicitly described as submature, we must imagine smaller parts of the higher domes and larger parts of the lower domes to retain their preglacial subdued forms, with only so much change as may have been caused by general weathering during the glacial period.

When all these significant featurles have been conceived, we may add that

FIG. 13.-NEREVI ON THE MARINE PLATFORM OF THE RIVIERA LEVANTE, LOOKING NORTH-WEST.

FIG. 14.-THE VILLAGE OF SESTEI LEVANTE, ON THE ISTHMUS OF A LAND-TIED ISLAND: THE PENINSULA OF PORTOFINO IN THE DISTANCE, LOOKING NORTH- WEST.

Snowdon, the highest domne of the group,.has been so greatly reduced by the excavation of four large and two smaller cwms in its flanks as to present only a skeleton of its former self; that its north-eastern, south-eastern, and south-western rounded ridges have been narrowed into sharp aretes; that its eastern cwm holds lakes at two levels, separated by a rock-step; that Mynydd Mawr, a fine dome but of less altitude than Snowdon, has two cwms of so moderate a size as to leave a



FIG, 15.-ENCROACHMENT OF A WAVE-CUT COVE ON THE NARROWED MARINE PLATFORM BETWEEN BOGLIASCO AND SORI, LOOKING NORTH-WEST.

FIG. 16.--THE RAILWAY STATION AT ZOAGLI, BlTWEEN TUNNELS IN CLIFFED PROMONTORIES, LOOKING SOUTH-EAST.



great part of its dome intact; but that its southern and north-eastern sides have teen cliffed by the strong over-deepening and widening of the neighbouring valleys; that several goo.l-sized, unconsumed rock-knobs obstruct an otherwise well-excavated trough on the south-east (valley of Afon Glaslyn), between the valley-floor rock-basins of two lakes (Gwynant and Dinas); that an uneven, low rock-step occurs in the chief trough on the south-west (valley of Afon Gwarfai) not far below a rock-basin lake (0Cwellyun), which, like the other basins, shows some delta-filling at its upper end; that the fine hanging lateral valley, which heads in the great cwm (Clogwyn) in the west face of Snowdon, has a small gorge cut in the slope where it opens in the side of the deeper main trough (Afon Gwarfai valley); and so on.

It is true that geographers and geologists are not yet agreed on the problem of glacial erosion, and it would therefore be prudent to precede the whole of the foregoing explanatory description with the statement that the writer finds the evidence in favour of glacial erosion irresistible; and, further, that he finds it possible to work out a series of ideal forms due to glacial erosion much in the same way that the series of ideal forms due to ordinary erosion has been worked out-that is, by a legitimate and logical combination of induction and deduction. It is then just as serviceable to desctibe the actual forms of a glaciated district in terms of the ideal forms of a cycle of glacial erosion, as to describe the actual forms of a normally eroded district in terms of the ideal forms of a normal cycle; or as to describe the actual forms of a coastal district in terms of the ideal forms of a marine cycle. The verity of glacial erosion is now so well established by the study of the forms of

glaciated mountains in many parts of the world that it savours of undue conser- vatism to omit such forms from the systematic method of description that has proved so helpful for other forms.

The foregoing description of the Snowdon group involves a departure from the normal cycle unlike the interruptions caused by crustal movement, which occurred in the case of the two coastal plails already considered. The departure from

normal conditions in the case of Snowdon does not appear to have involved any significant change in the altitude of the land, but only a tempvrary change in climate, whereby the snowfall was increased and glaciers were formed where none existed before or sioce. Such changes may be treated as accidents which disturb the regular progress of normal processes. It is important to point out that the duration of the glacial period in Wales, as measured by the work then accomplished, must have been a very small fraction of the du,'ation of a normal cycle of erosion. The glacial accident was therefore a brief one; the normal cycle is now again in progress.

It was stated in an early paragraph that land forms, treated as the surface of rock masses, may be described in terms of structure, process, and stage. It must now Ie added that the description of land forms, thus considered, must always be associated with two other elements: one of these is the active process, which works on the land form and causes its change; the other is the land waste produced by the action of the destructive process on the passive structural mass. In a cycle of normal erosion, we have weather and streams as elements of the active process; and locally weathered soil, sheets of creeping soil, alluvial fans, flood-plains, deltas, and so on, as elements of the forms assumed by the waste of the land on the way to the sea. In a cycle of glacial erosion we have weather, snow-fields, and glaciers as elements of the active process; and locally weathered superglacial rock waste, moraines of various kinds, drumlins, eskers, kames, and so on, as the forms assumed by the waste of the land in association with glacial erosion. In a cycle of marine erosion we have weather, waves, and currents acting on the coast; and beaches, sand-reefs, tidal marshes, and so on, as the associated waste form:. In a cycle of



Eo

? o~

0

E?i 0 o

i

o5

n

0 o

O

B

E~

o 0

.

I

E-

fc-

h 3 0

H 1

I

U2

0

W

p E O

^i O 1

p O O

Tl

U



solvent erosion, such as prevails in limestone regions, travertine deposits gain an importance among waste forms, even to the point of building up barriers across valleys and causing lakes and waterfalls, such as occur in Karst districts. The falls of Tivoli, near Rome, are of this origin. In the cycle of arid erosion, sand- dunes and loess deposits become of importance. In all these cases, the forms assumed by land waste vary systematically through the course of the cycle. In the normal cycle, for example, coarse rocky waste is usually associated with a young stage of the cycle, when valley-sides are steep; while fine waste prevails in the late stages, when the relief is faint and the slopes are gentle. A whole series of interesting considerations follow naturally upon the systematic description of the forms assumed by the waste of the land on the way to the sea, in association with the land forms on which the waste lies and with the processes that are acting upon it.

A final example may be taken from the Riviera levante, the mountainous Italian coast between Genoa and Spezia, illustrated in Figs. 13-22. We have here, as on the Adriatic coast, a combination of normal and marine erosion, and a slight movement after maturity was reached; but the results are quite unlike those already described, because of certain differences that accompany the similarities. The district includes a part of the Apennines, in which the strata, chiefly sandstones of fairly uniform resistance, are greatly deformed. It is highly probable that more than one cycle of normal erosion has taken place since the strata wele deformed; but we are first chiefly concerned with the last cycle but one, during which the mountains were very generally reduced by normal erosion to subdued forms, except where masses of resistant intrusive rocks occur, while a late mature sea-cliff was cut back along the shore-line. Then an interruption occurred: a very gentle tilting took place on an axis at right angles to the shore, producing a slight elevation to the northwest and a corresponding depression to the south-east; and the new cycle thus introduced has as yet reached only an early or submature stage. Now, as in the previous examples, this concise description may be expanded and explained.

The mountains along the coast must, when the first cycle was interrupted, have generally presented rounded forms, cloaked withi creeping waste, and dissected by irregular or insequent valleys of advanced development; the coastal cliffs must have evenly truncated all the spurs that approached the sea; as the cliffs are described as late mature, they must have gained a considerable height by being cut far back into the mountains; but at the same time they must have lost their youthful steepness, because the waste that would be shed from a high and steep cliff could not be disposed of by the waves that must have been weakened by rolling in to the shore across a broad and shallow platform of marine erosion; the streams had no deltas of significant size, because the whole shore-line was in retreat or retrogression.

Now the gentle tilting takes place. To the south-east the sea beats above the cliff-base and invades the valley mouths; at a score of miles from the axis of tilting the depression .suffices to submerge a low col, and convert an outlying ridge- end into an island. In the other direction, the marine platform, covered with a thin sheet of sea-laid waste, is revealed as a young coastal plain of increasing height and width to the north-west. The processes of normal and marine erosion then again proceed in their work upon the land mass in its new attitude, but as yet they have made only moderate progress.

Where the sea now beats on the face of the somewhat submerged cliffs, it steepens them, arid makes the shore-line more ragged than before, disclosing disordered rock structures; where the valley mouths have been drowned into bays, deltas are filling the bays and converting them into small triangular, beach-fronted, seaside


FIG. 19.-THE CHURCH AND CASTLE OF CAMOGLI, ON A ROCK-REMNANT OF THE CONSUMED MARINE PLATFORM, LOOKING NORTH.

FIG. 20.-THE VILLAGE OF CAMOGLI, CROWDED TO THE WATER'S EDGE.

THE SYSTEMLATIC DESCRIPTION OF LAND FORMS. 315

:iii:i : :.:-f .:;: , r



plains. Naturally enough, the largest river of the region, about ten miles south- east of the axis of tilting, had eroded the widest valley before the tilting took place; the slight submergence of this wide valley made the largest bay; but the large river has now aggraded the bay, forming the largest plain, along the front of which the waves break evenly on the longest beach of the district: and here stands Chiavari, the largest town between Genoa and Spezia. The delta-plain is indeed built forward somewhat outside of the bay-mouth, so that it now stretches right and left, a mile or so, in front of the steepened cliffs. The island a few miles further south-east is now cliffed on its outer side, and tied to the mainland by a beach -from its inner side, so as to form a peninsula. Farther south-east, there are only small delta-plains between great steepened cliffs, to the point that encloses the Gulf of Spezia. The railroad along this stretch of the coast runs through tunnels back of the cliffs for a large part of the way, coming out to breathe as it crosses the small delta-plains.

In the other direction, towards Genoa, the extended rivers have cut mature valleys across the marine platform and its gravel beds, and have therefore somewhat deepened their former valleys among the mountains, with the result of frequently making the mountain-sides steepest near the stream line; at the same time the former sea-cliff has become less steep by the creep of waste from its upper part to accumulate at its base; and the sea has cut away the outer part of the platform, so that its present border is a ragged, immature, beachless, harbourless cliff of moderate height. Near the axis of tilling, where the plain was necessarily low and narrow, it has been entirely consumed, and here the sea is now renewing its attack on the former cliff, undercutting it somewhat below the former base. Farther from the axis, where the coastal plain was broader and higher, a larger and larger share of it remains, so that villages are built on it; still farther north-west, the remnant of the plain is a mile or more wide, and its ragged cliffs are 300 or 400 feet high; nearly all of this height is cut in rock, b3neath the level of the gravels of the former sea-bottom; here Genoa lies, partly on the plain, partly in the mature valleys that have been cut across it.

At the axis of tilting stands the peninsula of Portofino. It is protected by a heavy conglomerate along its exposed front, and was therefore not worn back by the sea to the general cliff line in the first cycle. The delta-plains on the south-eastern side of the peninsula give open space for the towns of Rapallo and Santa Margherita. No deltas are found on its north-western side; and there the town of Recco is crowded to the shore-line at a valley mouth close to the new cut cliffs. The superb view from the summit of the peninsula includes nearly all the features here mentioned, but to appreciate the details of this malvellous coast, one must stop at successive stations and walk from village to village. The railway ride is tantalizing, because one hardly has time to enjoy a charming view before the train enters a cut or a tunnel. A few miles out from Genoa one may turn from the main road, up the narrow paths through terraced flower gardens to the olive groves, whence the openings disclose extensive vistas over the marine platform where Nervi is built upon it (Fig. 13), b3tween the long sloping ascent of the former sea cliff and the sharply undercut margin of the present coast. Here the railroad runs on the platform in shallow cuts, crossing the new valleys on high viaducts, as at Bogliasco (Fig. 17); but as the platform is narrowed by sea encroachment, some of the shore coves threaten to undermine the track, as between Bogliasco and Sort (Fig. 15). A little farther toward the axis of tilting, as between Sort and Recco, the platform is all consumed, and the new cliff undercuts the old one (Fig. 21); here the highway mounts the slope and the railway tunnels. In strong contrast to Nervi and Bogliasco, which find room for gardens about their villas, is Camogli, on the north-western side of



FIG. 21.-THE NEW SEA-CLIFF UNDERCUTTING THE OLD ONE, BETWEEN SORI AND RECCO; THE UNCONSUMED MARINE PLATFORM BY NERVI IN THE DISTANCE; LOOKING NORTH-WEST,

FIG. 22.-THE VILLAGE OF PORTOFINO, IN A BAY AT THE SOUTHERN CORNER OF THE PORTOFINO PENINSULA, LOOKING NORTH.


318 THE SYSTEMATIC DESCRIPTION OF LAND FORMS-DISCUSSION. 318 THE SYSTEMATIC DESCRIPTION OF LAND FORMS-DISCUSSION.

the Portofino peninsula; here the hills descend directly to the sea, and the tall houses are built up from the beach (Figs. 19 and 20); for the platform of farther north-west and the delta-pllains of farther south-east are both lacking, and the village site is therefore necessarily on the steep hillside at a deepened valley mouth.

After the axis of tilting is past we find the little village of Portofino (Fig. 22) built around a small bay in a corner of the peninsula, where the tributary valley is so small that the bay in not yet converted into a delta-plain. Farther on, the former cliffs are sharply undercut at the new sea-level (Fig. 18); here the highway must ascend to a considerable height above the shore-line in passing around the promontories, while the railway tunnels at a lower level (Fig. 16). Then comes the broad delta-plain of Chiavari, and next is the picturesque town of Sestri Levante on its isthmus (Fig. 14). Still farther on is Moneglia, where the new cut cliff at the end of a spur between two small valleys is now protected by the forward growth of the two confluent deltas; and finally comes Porto Venere, where this littoral range of the Apennines dips under water and ends. The whole district is a delightful field for geographical exercise and enjoyment.

T''he chief object of this essay is to persuade English geographers to look into what is here called the method of structure, process, and stage, and make trial of it in the description of land forms. The trial can be made in two ways: the observer himself may describe a given district by two methods, one being the method here recommended, the other being any other method-the empirical, for example-and he may then himself compare his descriptions as to lucidity and compactness. A more thorough test will be made if the two descriptions are sub- reitted to two competent readers, each of whom reads only one description and then proceeds to draw a map or diagram of the forms described, the maps afterwards to be compared as to expressiveness; it is desirable that no local names should be used in this test, so that the readers shall not know anything of the place described except what is contained in the descriptions. A still better experiment may be-made by selecting a standard empirical description of a district known to the experimenter, writing an explanatory description of it in the same number of words, and comparing the lucidity of the two accounts.

Before the paper, Dr. STRAHAN: You will all, I am sure, agree with me that the Department is to be congratulated on having this opportunity of hearing one of the greatest masters in the art of expounding geographical problems. The opportunity has arisen through Prof. Davis being now on his way home from Berlin after an exchange of professorial duties with Prof. Penck, an interchange which constitutes the most graceful compliment that could be paid by the universities of one country to those of another. I will not detain you, but will at once ask Prof. Davis to give us his paper.

After the paper, Dr. STRAHAN: I think I may call upon you, in the first place, to testify to your appreciation of the extremely clear illustration of land-forms and their origin which we have had placed before us this afternoon. I have great sympathy with Prof. Davis in his claim that the nomenclature should be, to a certain extent, self-explanatory. Such a nomenclature, used as it was by himself, appeared to me to be admirable, and to enable him to put, in a few precise words, matter which a less skilled lecturer would have used many sentences to express. Numerous different problems of erosion have been touched upon this afternoon, the consideration of which is likely to lead to an interesting discussion. I hope it will not be necessary to impose any limit, and trust to the good sense of the speakers to remember that there are others to follow them. I now invite discussion.

Sir JOHN MURRAY: I do not think I am quite in a position to open the

the Portofino peninsula; here the hills descend directly to the sea, and the tall houses are built up from the beach (Figs. 19 and 20); for the platform of farther north-west and the delta-pllains of farther south-east are both lacking, and the village site is therefore necessarily on the steep hillside at a deepened valley mouth.

After the axis of tilting is past we find the little village of Portofino (Fig. 22) built around a small bay in a corner of the peninsula, where the tributary valley is so small that the bay in not yet converted into a delta-plain. Farther on, the former cliffs are sharply undercut at the new sea-level (Fig. 18); here the highway must ascend to a considerable height above the shore-line in passing around the promontories, while the railway tunnels at a lower level (Fig. 16). Then comes the broad delta-plain of Chiavari, and next is the picturesque town of Sestri Levante on its isthmus (Fig. 14). Still farther on is Moneglia, where the new cut cliff at the end of a spur between two small valleys is now protected by the forward growth of the two confluent deltas; and finally comes Porto Venere, where this littoral range of the Apennines dips under water and ends. The whole district is a delightful field for geographical exercise and enjoyment.

T''he chief object of this essay is to persuade English geographers to look into what is here called the method of structure, process, and stage, and make trial of it in the description of land forms. The trial can be made in two ways: the observer himself may describe a given district by two methods, one being the method here recommended, the other being any other method-the empirical, for example-and he may then himself compare his descriptions as to lucidity and compactness. A more thorough test will be made if the two descriptions are sub- reitted to two competent readers, each of whom reads only one description and then proceeds to draw a map or diagram of the forms described, the maps afterwards to be compared as to expressiveness; it is desirable that no local names should be used in this test, so that the readers shall not know anything of the place described except what is contained in the descriptions. A still better experiment may be-made by selecting a standard empirical description of a district known to the experimenter, writing an explanatory description of it in the same number of words, and comparing the lucidity of the two accounts.

Before the paper, Dr. STRAHAN: You will all, I am sure, agree with me that the Department is to be congratulated on having this opportunity of hearing one of the greatest masters in the art of expounding geographical problems. The opportunity has arisen through Prof. Davis being now on his way home from Berlin after an exchange of professorial duties with Prof. Penck, an interchange which constitutes the most graceful compliment that could be paid by the universities of one country to those of another. I will not detain you, but will at once ask Prof. Davis to give us his paper.

After the paper, Dr. STRAHAN: I think I may call upon you, in the first place, to testify to your appreciation of the extremely clear illustration of land-forms and their origin which we have had placed before us this afternoon. I have great sympathy with Prof. Davis in his claim that the nomenclature should be, to a certain extent, self-explanatory. Such a nomenclature, used as it was by himself, appeared to me to be admirable, and to enable him to put, in a few precise words, matter which a less skilled lecturer would have used many sentences to express. Numerous different problems of erosion have been touched upon this afternoon, the consideration of which is likely to lead to an interesting discussion. I hope it will not be necessary to impose any limit, and trust to the good sense of the speakers to remember that there are others to follow them. I now invite discussion.

Sir JOHN MURRAY: I do not think I am quite in a position to open the


Article Contentsp.300p.301p.302p.303p.304p.305p.306p.307p.308p.309p.310p.311p.312p.313p.314p.315p.316p.317p.318

Issue Table of ContentsThe Geographical Journal, Vol. 34, No. 3 (Sep., 1909), pp. 241-360Explorations in Central Asia, 1906-8 (Continued) [pp.241-264]Explorations in Central Asia, 1906-8: Discussion [pp.264-271]The Western Pacific: Its History and Present Condition [pp.271-288]The Western Pacific: Its History and Present Condition: Discussion [pp.288-290]Further Antarctic Reports of the Expedition of 1901-1904 [pp.290-297]The Observation of Air Temperature in the Tropics [pp.298-300]The Systematic Description of Land Forms [pp.300-318]The Systematic Description of Land Forms: Discussion [pp.318-326]ReviewsEuropeA Lincolnshire District [p.327]Ireland [pp.327-328]Ice-Conditions on Lake Balaton [pp.328-329]

AfricaEthnography of German East Africa [pp.329-330]The Sanga-Shari Borderlands [pp.330-331]The Canaries [pp.331-332]

AmericaLater Phases of the Pele Eruption [p.332]

Australasia and Pacific IslandsEthnology of New Guinea [pp.333-334]

Polar RegionsAntarctic Pictures [pp.334-335]

GeneralDensities of Population [pp.335-336]Life in the Navy [pp.336-338]

The Monthly Record [pp.338-347]Geographical Literature of the Month [pp.348-356]New Maps [pp.356-360]

the systematic description of landforms

Documents